Of the world’s 1.3 billion Muslims, around 170 million are Shia. The largest populations of Shia Muslims are found in India, Iran, and Iraq. Shiism developed out of a dispute between the Prophet Muhammad’s followers over who would succeed him as the leader of the Muslim community. After the Prophet’s death in 632 C.E., some believed that the new leader should come from the Prophet’s family. This faction supported Ali Ibn Abu Talib, Muhammad’s cousin and son-in-law. Ali’s faction was overruled, and the majority chose Abu Bakr, Muhammad’s uncle, to succeed Muhammad and become caliph. Ali’s partisans continued to support Ali’s leadership claim, however, as he was passed over two more times—first in 634 C.E., in favor of Umar, and again in 644, in favor of Uthman. Ali was finally named the fourth caliph in 656 after Muslim soldiers murdered Uthman. Ali’s supporters later became known as Shiite Ali, the “partisans” of Ali.

Ali’s leadership of the Muslim community was beset with difficulty from its first days. One of Uthman’s relatives, Mu’awiya, demanded retribution for his murdered kinsman. The murder of Uthman thus provided a pretext for Mu’awiya to attempt to retake the caliphate for the Ummayad clan, to which Uthman and Mu’awiya both belonged. After a period of conflict between Ali and Mu’awiya, a portion of Muslims blamed both leaders for the continued unrest, and attempted to assassinate both of them. They failed to murder Mu’awiyah, but their attack on Ali was successful, and he died of his wounds in 661 C.E. After Ali’s death, his eldest son, Hassan, became caliph. In the interest of avoiding further bloodshed between Muslims, Hassan agreed to abdicate in favor of Mu’awiya.

In 680, Mu’awiya arranged for his son Yazid to succeed him as caliph. In response, Ali’s second son, Hussein, raised an army and led a rebellion against Yazid to reclaim the caliphate for the Prophet’s family. Though vastly outnumbered, Hussein refused to surrender. He was killed in battle with Yazid’s forces near Karbala.

The martyrdoms of Ali and Hussein permeate Shia religious practice and political consciousness, contributing to the Shia sense of themselves throughout history as righteous followers of the Prophet’s true path, persecuted by usurpers. This model of persecution, resistance, and martyrdom is replayed throughout Iraqi Shia history. The persecutors have come in various guises: Sunni Ottomans, British occupiers, the British-installed Sunni monarchy, the Baath Party, Al Qaeda, and the U.S. military. The experiences of Iraqi Shia at the hands of these oppressors fit neatly within, and greatly strengthen, this conceptual framework.

The majority of Shia belongs to a sect known as “Twelvers,” so called because of their belief in the 12 Imams, leaders descending from the Prophet Muhammad. They believe that the 12th Imam—Muhammad al-Mahdi, known as “the Hidden Imam”—was hidden by God in a spiritual realm, and that his return will herald an era of peace and justice. In the absence of an earthly ruler, Shia developed a system of religious accreditation and leadership in which individuals choose a marja al-taqlid, or object of emulation, from among recognized clerics to act as their spiritual guide. Devout Shia address questions regarding faith practices and proper conduct to their chosen marja, and they are required to follow his decisions, known as fatwas.

Education in the Shia seminaries is a rigorous process. Students generally begin their studies between the ages of 14 and 20. There are three levels, or study cycles, each taking between three and six years, and students advance through acclaim for his understanding of the Quran and hadith (sayings of Muhammad), and of the Arabic language, by consensus of his teachers and, later, his students. Unlike the Imams, who were believed to have possessed a supernatural ability to understand the Quran and thus did not need to rely upon human reason, Shia scholars have developed a process of independent interpretation of religious matters, known as ijtihad. Once a scholar achieves the rank of mujtahid, he is granted a diploma and permitted to rule on religious questions in edicts known as fatwas.

The two leading centers of Shia learning in the modern world are Najaf, in southern Iraq, and Qom, in northern Iran. As the site of the tomb of Imam Ali, Najaf was for centuries the center of Shia learning in the Middle East. After the Iranian Revolution in 1978, Qom began to replace Najaf as the chief seminary of the Shia world, both because of the substantial government resources provided for this purpose and because of the increasingly oppressive atmosphere for Shias in Saddam Hussein’s Iraq.